MAPK1 and cancer: In unstimulated cells RKIP, Raf Kinase Inhibitor Protein, is bound to Raf and prevents MEK phosphorylation (Park et al., 2005). Following mitogenic stimulation, RKIP dissociates from Raf to allow MEK and ERK activation (Kolch, 2005; Shin et al., 2009) RKIP functions as a metastasis suppressor in multiple solid tumor types such as prostate and breast cancer (Keller, 2004). RKIP is down-regulated in some types of cancers and is associated with resistance of cancer cells to anti-neoplastic treatments (Granovsky and Rosner, 2008).